Sinfest has had a tendancy to focus excessively on feminism since 2011, resulting in a very Broken Base.
Pastel Defender Heliotrope was rather unsubtle to readers with ideas of the oppression of women and sexual identities and evils of religion. To make sure ALL the bases were covered, JDR reveals in the ending that the entire thing was started because some robots wanted to ask permission to do we're-not-sure-what but no one was around to ask. Just to make sure that she's striking out against anti-piracy legislation in the most Anvilicious way possible.
Tim Buckley's self insert into thisCtrl+Alt+Del strip, where he rants at Jack Thompson. Also contains the irony that Tim is threatening Jack Thompson for saying that gamers are violent and that his video game obsessed main character performs acts of extreme violence on a regular basis (not to mention that his little spiel ends with the phrase "don't fuck with us").
Dominic Deegan drops numerous anvils of "intolerance is bad!" We know this because everyone who acts intolerantly is usually portrayed as irredeemably evil, not to mention the fact that something horrible will probably happen to them before the end of the arc.
The anvil is lightened by some of the reasons for the cultural conflict between Callan and the orc tribes being very obviously irreconcilable: on the human side the knights are oppressive, violent, and have the actual authority to make legally binding rulings. On the orc side, necromancy is considered a normal magical practice and rape is a standard legal tool for compelling compliance. Dominic's family's wealthy, powerful, and generally privileged perspective is the viewpoint of the comic, and the reader is seeing how he feels about the situation.
Made fun of in thisNip and Tuck comic. Nip, a B-movie writer/star, talks about why he does not do romance in his movies. He explains how bad Hollywood romance plots are. He mentions My Fair Lady and The Taming of the Shrew and how a girl with nothing wrong with her is run through a "Magic Makeover Machine" which is supposed to end up with the hero seeing her true inner beauty. The illustration that accompanies the talk shows a simple caricature of a woman getting smashed by a hydraulic press with the word "AESOP" written on it.
While Chris is usually pretty good about it, Misfile has a few strips that make it more than clear that Ash's character is supposed to be read as a trans boy, and that everything he goes through is supposed to drive home An Aesop about accepting trans people, except for the ones that are supposed to drive home An Aesop about accepting gay people.
Lampshaded/parodied here in Tally Ho. With an actual anvil no less.
Viciously mocked with the "Final Thoughts" in The Adventures of Dr. McNinja. Almost every single moral given is completely irrelevant to the story's content and gets comically derailed in some fashion.
Sandra and Wooused to be pretty blunt with its anti-animal cruelty and pro-environmentalist messages. It also had one chapter that was fairly anvillicious about the very, very obscure and specific message of anti-people-who-think-diabetics-injecting-insulin-are-doing-drugs.
Subnormality is incredibly guilty of this. In almost every strip.